B. Sc. University of Toronto 1991
Ph. D. University of British Columbia 1997
Postdoc, Weizmann Institute of Science 1997-1999
Research Associate, University of Toronto 1999-2000
Postdoc, Tokyo University 2000-2001
Faculty, Memorial University of Newfoundland 2001-

Research - Condensed Matter Theory

I study electronic, magnetic and structural properties of solid state
materials. Here are a couple of recent topics.

Tb2Ti2O7:
Quantum spin configurations

Tb2Ti2O7 is a spin liquid
which persists to very low temperatures,
T< 50 mK.
The rare earth (terbium) ions sit on the vertices of
a corner-shared tetrahedral network. The
ground state of the Tb spins is doubly degenerate, which can
be visualised as classical spins that point into or out of
the tetrahedra. However, these spins are not classical in
any approximation.
First, diffuse neutron scattering can only be explained if
there are "quantum fluctuations" of the spins, that is, some
probability that they can point in other directions.
Second, the actual spin configuration is quite unlike the one
shown. Rather, it is a linear combination of all
similar-looking states such that the different
spins states are entangled.

Pr-filled Skutterudites:
Unconventional Superconductivity

The materials
RT4X12 are known as "filled skutterudites", where R is a rare earth
element (La, Ce, Pr, Nd, Eu, Yb), T are transition elements (Fe, Ru or
Os) and X are pnicogens (P, As or Sb).
The pnicogens form the octahedra, with the transition element inside,
and the spaces between octahedra are filled by the rare earth elements.
The materials
in this series exhibit a wide range of
behaviour: superconductivity in the La-compounds, semiconductivity in
the
Ce-compounds, non-magnetic ordering and Kondo behaviour in the
Pr-compounds, and ferromagnetism in the Nd- and Eu-compounds.

PrOs4Sb12 is the first Pr-based heavy fermion
superconductor and the first among the family of filled skutterudite
compounds.
The superconducting order parameter is thought to be unconventional:
it involves spin-triplet pairing of the electrons with broken
time reversal symmetry. This leads to a very unusual superconducting
gap function, with two different branches (centre). The lower branch of the
gap function has four nodes which do not occur on lines of high symmetry (right).